The present invention relates to a process for refining glycerine, and more particularly to a process for reducing the levels of impurities such as glycerine-based acetals and ketals, and particularly 4-hydroxymethyl-1,3-dioxanes; 5-hydroxymethyl-1,3-dioxolanes and 4-hydroxymethyl-1,3-dioxolanes, (hereinafter collectively referred to as acetals and/or ketals) in glycerine.
Glycerine, also referred to as glycerol, i.e. 1,2,3-propanetriol, has been a chemical of commerce for many years. Derived both as by-product from soap manufacture and synthetically, glycerine is used in many diverse applications, such as in alkyd resins, cellophane, tobacco processing, drugs, cosmetics, and in food and beverages.
There are three major routes to synthetic glycerine, each starting with propylene. One route involves four process steps--the chlorination of propylene to allyl chloride, the chlorohydrination of allyl chloride to glycerol dichlorohydrins, the hydrolysis of the dichlorohydrins to epichlorohydrin, and the hydrolysis of epichlorohydrin to glycerine. A second route is based upon three process steps--the oxidation of propylene to acrolein, the hydrogenation of acrolein to allyl alcohol, and the hydroxylation of allyl alcohol to glycerine. The third route also employs three steps--the epoxidation of propylene to propylene oxide, isomerization of propylene oxide to allyl alcohol, and the hydroxylation of the allyl alcohol to glycerine.
A number of methods for purifying glycerine of small amounts of undesirable compounds have been proposed over the years including e.g., catalytic hydrogenation in an acid medium, and treatments with chemicals such as hydrogen peroxide, with sulfuric acid and activated carbon, and with sodium carbonate. Further the concentration and/or purification of glycerine by extraction with certain solvents is known, e.g. the use of certain hydrocarbons, ethers, esters and chlorinated solvents is disclosed in U.S. Pat. No. 2,154,930; the use of tert-amyl alcohol is disclosed in U.S. Pat. No. 2,436,209 and the use of solvents including certain aliphatic alcohols, aromatic alcohols, cyclic amines, ketones, ethers, aldehydes, and esters is disclosed in U.S. Pat. No. 2,479,041. A distillative process for separating glycerine from certain acetals and/or ketals is disclosed in U.S. Pat. No. 4,360,407.
Applicants have found that some commercially available glycerine contains small amounts of acetals and/or ketals, which acetals and/or ketals should desirably be removed to very minimal levels for some applications. They have further discovered a relatively simple extraction process with a unique solvent to accomplish this.